Abstract
For the prestressed concrete steel bar, a smaller amount of relaxation is required together with higher mechanical properties.
We studied on the relaxation property of prestressed-concrete steel bars which had heat treated carbon steel, spring steel, and low alloy steel to 115kg/mm2 and 130kg/mm2 in ultimate strength.
In the experiment, we observed that S30C, S40C, S50C relaxed over 3% for 20 hours under the initial stress of about 80% of actural yield strength, SAE1041, SCr-2 relaxed 2 to 3% and SCM2, SCM4, SUP9 relaxed about 1%
As for the relation of the relaxation with mechanical properties, it is recognized that the amount of relaxation is inclined to decrease with the increases of ratio σS/σB and of elongation. It was concluded that, the steel bar which had tempered at high temperature and was sufficient in regard to mechanical properties, was excellent also from the view point of relaxation.
